Eggs have a shell that offers limited protection from bacterial penetration. A number of egg characteristics influence penetration, growth and spoilage by micro-organisms. Before hatching, the egg passes through the end of the intestinal tract and thus is subjected to the micro-flora therein. In addition, eggs are highly sensitive to contamination by pathogenic microorganisms if not stored in proper conditions. Contaminants, like bacteria or molds, have the potential of spoiling the eggs or posing serious health risks to their consumers. Methods of preserving eggs for prolonged periods include refrigeration, cooking, freezing, drying and powdering, pasteurization and pickling. Pickled eggs are prepared by immersing cooked peeled eggs in an acidic solution, like vinegar, typically also containing salt, sugar, spices, or any combination of these ingredients. Methods for pickling raw eggs, or raw egg yolks, are also available. Pickled eggs prepared by such methods can be preserved for a period ranging from a few weeks up to several months.
The ingredients of the pickling solution, in addition to their contribution to the product's taste, odor, color and texture, have an active role in preventing the growth of contaminants. The optimal pH for the growth of most micro-organisms is near the neutral point (pH 7.0). As a result, the acidity of the pickling solution is adjusted to a pH lower than 7, thus contaminant growth is impeded.
Addition of sugar and salt increases the solute concentration in the pickling solution beyond the solute concentration in the contaminant cells, thus rendering the solution “hypertonic”; in other words the addition of solutes to the pickling solution increases its osmotic pressure. Thus, the solutes in the solution are referred to as osmotic agents. Since the osmotic pressure inside the contaminants' cells is lower than the osmotic pressure of their environment, water exits the contaminants' cells, thus lowering their vitality.
Such methods are disclosed for example in U.S. Pat. No. 1,234,567 and EP 1,234,567.